A variety of flexible cannulas have been produced that are positioned to contact the nasal-labial area between the patient's upper lip and nostrils. Even though many of these cannulas were made of soft, flexible plastic, the wearer frequently encountered discomfort because a cannula is usually worn for a prolonged period of time. This results in continued contact of the cannula with the wearer's facial tissues, especially at the philtrum and around the unprotected nasal-labial area, thereby causing irritation and inflammation.
The structures of conventional cannula devices may be categorized into two general groups.
The first group utilizes a unitary member that includes a main tubular portion and a pair of tubular nasal prongs integrally connected to and in fluid communication with the main tubular portion. The main tubular portion has opposite ends which are connectable to flexible auxiliary oxygen supply tubes that are looped over the patient's ears and which themselves are in fluid communication with a pressurized source of oxygen. As is known, the nasal prongs are inserted into the nares of the wearer to deliver a low flow of oxygen to the patient's respiratory tract. The main tubular portion of these devices spans much if not all of the length of a wearer's upper lip. In so doing, the main tubular portion exerts contact pressure across much of the patient's upper lip. Under these circumstances, a patient usually begins to experience discomfort in a relatively short period of time even if the cannula itself and the auxiliary oxygen supply tubes connected thereto are designed to deliver relatively low flows of oxygen, i.e., they not particularly robust, stiff or heavy in weight. Examples of cannula devices and assemblies constructed in accordance with this first group may be found in, for example, U.S. Pat. Nos. 2,868,199; 3,643,660; 3,802,431; 4,106,505; 4,156,426; 5,400,776 and 5,794,619 and in published U.S. Patent Application Publications Nos. U.S. 2001/0031929 A1 and U.S. 2002/0112730 A1.
The second group involves a harness member that does not itself convey oxygen but which retains flexible auxiliary oxygen supply tubes in such a way that their discharge outlet ends define nasal prongs. However, the harness members of these devices also typically span all or most of the length of a patent's upper lip whereby the devices, even for light-duty gas delivery applications, produce the same patient discomfort problems as the cannula devices of the first group. Examples of cannula devices constructed according to the second group may be found in, for example, U.S. Pat. Nos. 2,931,358; 3,400,714; 4,278,082; 4,648,398; 4,790,308; 4,818,320 and 5,533,506.
Published United States Patent Application Publication No. U.S. 2002/0046755 A1 (the '755 publication) discloses various embodiments of nasal cannulas that fall into one or the other of the aforementioned groups, as well as other embodiments that are not as readily classifiable. However, none of the nasal cannulas disclosed in that publication describe a device that would be comfortable to a patient under the high flow conditions a patient would experience under positive airway pressure therapy, e.g., continuous positive airway pressure (CPAP) or bilevel positive airway pressure (BiPAP), that is often prescribed to patients suffering from Obstructive Sleep Apnea (OSA). For example, according to one embodiment of cannula taught in the '755 publication, a relatively narrow connector member that would rest against a patient's upper lip is integrally attached to the flexible auxiliary oxygen supply tubes whereby the ends of the tubes would function as nasal prongs that elastically engage the user's nasal septum inside of the nostrils. As used herein, the term “nasal septum,” or simply “septum,” means the wall that divides the nasal cavity into halves which terminate at the nostrils. At its front or anterior portion the septum is a firm but bendable structure made mostly of cartilage that is covered by skin. In order to deliver respiratory gas flow to a cannula that would be therapeutically desirable to maintain a typical adult patient's respiratory passageways open during OSA, for example, conventional auxiliary oxygen supply tubes must have an outer diameter of up to about ¼ inch (0.635 cm). Tubes of this caliber, when inserted short distances into the nostrils (as they must be so as not to harm the internal nasal tissues), would be quite obtrusive, stiff and uncomfortable to the user, especially when in elastic contact with the user's septum. Such discomfort would, in turn, detrimentally impact the patient's compliance with his or her prescribed positive airway pressure regime and, therefore, reduce the overall effectiveness of therapy.
U.S. Pat. Nos. 4,782,832; 5,042,478; 5,134,995; 5,269,296; 5,535,739; 5,687,715; 5,752,510; 6,431,172 and 6,478,026, as well as published United States Patent Application Publication No. U.S. 2002/005935 A1, described nasal cannulas for positive airway pressure therapy. However, the cannula devices disclosed in these documents are quite large and cumbersome. Indeed, many are designed to cover and/or seal the patient's nostrils. Consequently, they too are not conducive to optimum patient therapy compliance.
An advantage exists, therefore, for respiratory therapy system including a nasal cannula assembly that is compact, lightweight and fabricated from highly flexible material. So constructed, the assembly would be comfortable for patients that undergo respiratory therapy involving the administration of pressurized respiratory gases for extended periods of time, including therapy involving the administration of pressurized respiratory gases at the high flow rates that are useful in positive airway pressure therapy.